Method of sealing containers



Jan. 27, 1970 F. E. WRIGHT METHOD OF SEALING CQNTAINERS Filed Jan. 3. 1967 2 Sheets-Sheet 1 FIG. 2

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F E WRIGHT ATT Rim Jan. 21, 1970 F. E. WRI GHT 3,491,509

METHOD OF SEALING CONTAINERS Filed Jan. 5, 1967 2 Sheec-Sheet 2 I \I FIG. 3

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I I I l I F f 1 I I A T TZZ/VEVS United States Patent C) 3,491,509 METHOD OF SEALING CONTAINERS Franklin E. Wright, Scriba, N.Y., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Jan. 3, 1967, Ser. No. 606,717

Int. Cl. B65b 51/14 US. Cl. 53-39 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method of sealing a cover sheet on a container.

In modern merchandising it is desirable to package certain types of products, such as food products, in attractive protective packages. One of the most widely used packaging techniques for food is to thermoform a container out of a sheet of substrate, fill the recess with the material to be packaged, and then place a cover sheet over the filled container and seal the cover sheet around the edges of the container.

In order to produce a finished package that possesses satisfactory asthetic qualities and, additionally, is resistive to punctures and tearing, the cover sheet must be drawn taut over the container. If the cover material is not drawn taut, it will sag into the package and destroy the marketability of the product due to its unsightly appearance. In addition, the sagging or drooping of the cover sheet will result in damage to the goods during handling.

Prior art attempts to solve the problem of drawing the cover sheet taut were confined to physically pulling it taut before sealing by the aid of mechanical devices to place a tensile force in the cover sheet. This method is unsatisfactory because it is difiicult to draw the cover sheet tight enough to prevent sagging after sealing and still conduct the sealing operation.

This invention is superior over the prior art in that the cover sheet is drawn taut in conjunction 'with the sealing operation. Consequently, the steps of pulling the cover sheet taut and then sealing the cover sheet have been combined into one single step. Additionally, this invention provides for drawing the cover sheet taut in a more effective and less complicated and costly manner.

In one embodiment, this invention comprises a method whereby a recessed thermoformed plastic tray or container is filled with a packaged product and the cover sheet is applied in a taut position. The cover sheet is drawn taut by placing the cover sheet over the filled recessed container, and without stretching or pulling the cover sheet a heated sealing tool descends and deforms the edge of the container and that portion of the cover sheet over the edge into a groove in a plate or member. The heat seals the cover sheet to the container by melting the two together. The central portion of the cover sheet is thereby drawn taut and tightened over the filled container. The heat from the sealing function causes the cover sheet and container edge to become permanently deformed. Thus, when the sealing tool is withdrawn, the cover sheet remains taut. If the container edge and cover sheet were not permanently deformed and returned to the original flat position, the cover sheet would not be drawn taut. Thus, the permanent deformation is required to keep the cover sheet taut after it has been first drawn taut by the action of the sealing tool.

Accordingly, it is an object of this invention to provide a method of sealing the cover sheet on a container in a taut position.

Another object of this invention is to provide a method of drawing the cover sheet taut and sealing same on a container in one single step.

Other objects, advantages, and features of this invention will be readily apparent to those skilled in the art fgom the following description, drawing, and appended c aims.

The attached figures represent one embodiment of the invention.

FIGURE 1 represents a plan view of a thermoformed container, filled with a product covered with a cover sheet.

FIGURE 2 represents an elevation view of a crosssection of FIGURE 1 taken at the indicated plane.

FIGURE 3 represents the edge of a thermoformed container being placed in position for filling with the product to be packaged therein.

FIGURE 4 represents the container after it has been filled and the cover sheet applied.

FIGURE 5 represents the sealing tool moving down to seal the package and to draw the cover sheet taut.

FIGURE 6 represents the edge and cover sheet being deformed by the sealing tool and the cover sheet thereby drawn taut. The cover sheet is being sealed during this step.

FIGURE 7 is a larger view of the deformation and sealing step being conducted.

With reference to FIGURE 1, there is indicated a plan view of one embodiment of a packaged product made by the method of this invention. Specifically, in FIGURE 1 there is indicated container 10. Container 10 can comprise any container that will permanently deform at the edges and thoroughly bond to a cover sheet when the edges are subjected to deformation and heat. Container 10 must, however, be equipped with flat peripheral edges suitable for bonding a cover sheet thereto. Particularly, containers made from thermoforming thermoplastic substrate are suitable for use in this invention. More specifically, substrates constructed of polyvinyl chloride, polystyrene, polypropylene, and polyethylene are entirely satisfactory for use in this invention. In one embodiment, containers were thermoformed from a substrate of polyethylene made according to the method of Hogan and Banks, US. Patent 2,825,721.

Additionally indicated in FIGURES 1 and 2 is a prodnet 11 packaged according to this invention. Any product that will not chemically or physically destroy the package media can be used in the invention. Specifically, food products are applicable for use in this invention. Additionally, there is indicated in FIGURES 1 and 2 cover sheet 12. Cover sheet 12 can comprise any transparent or nontransparent material of sufficient tensile strength so as to be pulled taut and possessing properties permitting it to be bonded to container 10 by the application of heat. Obviously, a satisfactory cover material will depend upon the material from which the container is to be constructed, since a thermally induced bonding is necessary according to this invention. Specifically, polyethylene or polyethylene bonded to cellophane on a polyester film is a satisfactory transparent cover material. Additionally, paper laminated to polyethylene provides a satisfactory nontransparent cover material. In an alternate embodiment, metal foil was laminated to polyethylene and used as a nontransparent cover material. In one further embodiment, a nontransparent cover sheet was constructed by laminating metal foil to paper and then laminating this to polyethylene. If desired, the labels used to market the goods can be used in place of the paper.

FIGURES 3-7 indicate the method of the invention being used to manufacture the packaged product illustrated in FIGURES 1 and 2.

Referring to FIGURE 3, the flat edge 13 of a container 10 is disposed on a die 14, which is equipped with a groove 15. According to a preferred embodiment of this invention, the die 14 underlies the entire edge 13, and thus corresponds to the geometry of the container itself and completely encircles the container. Stated another way, die 14 is square if the container is square, rectangular if the container is rectangular, and circular if the container is circular. The above embodiment is preferred because the cover material can be pulled taut in one single operation. If there is a die such as 14 on each side of a square or rectangular container, the cover sheet could be pulled taut in one direction, then the two unsealed edges could be placed on two more dies such as 14 and the cover sheet drawn taut in the other direction. Although eifective for square or rectangular articles, this method produces an additional step and is less desirable than the preferred embodiment where die 14 surrounds container 10 and the sheet is pulled taut in one single step.

In FIGURE 4, the container 10 is filled with a food product 11 or other material to be packaged, and cover sheet 12 placed thereon. The sealing operation is now ready to be effected.

In FIGURE there is illustrated a sealing tool 16 having a projection overlying the cavity 15, and mounted for reciprocating motion:

In FIGURE 6, the sealing tool 16 is extended into the cavity 15 thereby deforming the edges of the cover sheet and container by forcing them into the cavity 15 in die 14.

FIGURE 7 indicates in detail the deformation procedure, as well as the sealing and drawing taut features. As will be noted in FIGURE 7, sealing tool 16 has descended downward in a direction generally perpendicular to edge 13 only so far as to somewhat depress the center portion of container edge 13 and cover sheet 12. According to this invention, the portion of the edge on the inward and outward sides of the depressed center portion are confined by the die 14 and prevented from moving by the sealing action. It is to be noted that the degree of deformation can be adjusted to the particular materials being used and the needs of the user. Since according to this invention the cover sheet 12 is to be pulled taut, there must be sufiicient deformation occurring to pull the cover sheet taut. When heavier cover sheets are to be used, more deformation will be required to pull them taut. It is further to be noted that the deformation can be as illustrated in FIGURE 7 or sealing tool projection 17 can be constructed so as to fit snugly within cavity 15, thereby deforming the container and cover sheet to substantially the same geometry as the cross-section of cavity 15. If this stamping function is employed, the cavity 15 and sealing tool projection 17 are reduced in size from that illustrated in FIGURE 7. In this case, close tolerances must be observed in the manufacturing operation so as to properly place sealing tool projection 17 within cavity 15. Additionally, close temperature control must be maintained as to container edge 13 so as to maintain the edge in a condition to deform out not break during the rather severe deformation incorporated into the stamping function.

In a preferred embodiment, the deformation is effected by lowering a relatively small sealing tool projection 17 into a comparatively large recess such as 15. As a result of this, a moderate deformation such as illustrated in FIGURE 7 is effected. While the width and depth of cavity 15 can vary with respect to the width and length of sealing tool projection 17, in one embodiment cavity 15 was 0.141 inch wide and 0.050 inch deep. The sealing tool projection 1.7 was 0.062 inch wide and 0.125 inch long.

Of course, other sizes and geometries of grooves and seal ing tool projections can be used without departing from the scope of this invention.

After the proper deformation for the needs of the user has been effected, container edge 13 and cover sheet 12 are heated as a result of sealing tool 16 and sealing tool projection 17 being maintained at a sufficient temperature to seal cover sheet 12 to container edge 13 by melting the two together. The temperature required to be maintained in sealing tool projection 17 so as to properly bond cover sheet 12 to container edge 13 without melting or damaging either the cover sheet or container edge will depend on the material selected by the user. Generally, a temperature of from 290-500 F., and preferably from 310325 F., is maintained in sealing tool projection 17. In an alternate embodiment, the heat necessaryfor sealing can be supplied by maintaining die 14 at the proper temperature. Sealing tool 16 or die 14 are heated by an externally applied electrical potential (not shown), in one embodiment.

Sealing tool projection 17 must remain in the position of FIGURE 7 for a length of time suflicient to transfer heat from sealing tool projection 17 through cover sheet 12 to container edge 13. The length of time required will vary with the temperature to be maintained in sealing tool projection 17 and the materials selected for the container and cover sheet. In one embodiment, sealing tool projection 17, of the dimensions described earlier, was held in the deforming position for 0.75 second. The time the cover sheet and edge are held in the deformed position is preferably in the range from 0.2 to 4 seconds. The range of 0.6 to 1.5 is even more preferable.

As will be noted in FIGURE 2, container edge 13 and cover sheet 12 remain deformed to some extent after sealing tool projection 17 is removed. The necessity of remaining deformed results from the fact that only when there is less than total recovery after the deforming step, i.e. some deformation, will the cover sheet 12 remain taut. Varying amounts of recovery after the deforming step can be tolerated depending upon the elasticity of the cover sheet 12.

This invention is equally applicable to placing a sheet in a taut position, whether it be placed over a container or not;

This invention is thus broadly applicable to placing a sheet in a taut position over a container.

Various modifications of this invention can be made in view of the foregoing disclosure and the appended claims without departing from the spirit or scope thereof.

EXAMPLE container for packaging food products was constructed by thermoforming a flat sheet of polyethylene of .960 gm./cc. made according to the method of Hogan and Banks, U.S. Patent 2,825,721, into a sloping wall rectangular tub 5% inches long by 4% inches wide by 1 /2 inches deep with fiat peripheral edges 0.015 inch thick and about 4 inch wide. This container was then placed within a framework which supported the peripheral edges of said container. The framework had a recess therein 0.141 inch wide by 0.050 inch deep. The container is then filled with sliced luncheon meat and a 1 /2 mil thick polyethylene coated cover sheet of polyester was placed over the filled container with the polyethylene surface of the cover in contact with the container edge. The cover sheet was not stretched or pulled in any mechanical manner, but was merely placed on the filled container and allowed to sag slightly due to its weight. A sealing tool, having a project1on 0.062 inch wide by 0.125 inch long constructed in a rectangular manner, was lowered so as to depress the container edge and cover sheet edge into the groove in the earlier described rectangular framework. The sealing tool pro ection was maintained at a temperature of 350 F. and held in the depressed state for 0.75 second. As a result, the cover sheet and container edge were deformed 0.015 inch from their normal planes. The polyethylene cover sheet was pulled taut by virtue of the deformation and sealed to the container edge by virtue of the heated sealing tool projection. A permanent deformation from the normal plane of the surfaces and measured at right angles to the surface was noted to be 0.007 inch. The cover sheet remained taut through subsequent handling and marketing operations.

What is claimed is:

1. A method of heat sealing a cover sheet over a container comprising the steps of:

(a) positioning the edge of a cover on a fiat peripheral edge of a recessed filled container, said edges being formed from heat sealable plastic material;

(b) depressing the center portion of said edge of a cover and said container edge in a direction generally perpendicular thereto while confining the portion of said flat edge on the inward and outward sides of said center portion, said central portion of said edges being thereby deformed and the central portion of the cover sheet being thereby tightened over the filled container; and

(c) heating the deformed portions of said edges to a heat sealing temperature to bond the cover sheet to the container edge, said heat also causing a permanent deformation in said container edge and cover sheet bonded thereto whereby said cover sheet remains taut over said container as a consequence of said deformation after removal of the depressing force.

2. The method of claim 1 wherein said container and edge are constructed of a material which comprises polyethylene; wherein said cover sheet comprises polyethylene.

References Cited UNITED STATES PATENTS 2,012,529 8/1935 Eldredge 53287 X 2,018,705 10/1935 Conti 5339 X 2,146,831 2/1939 Maxfield 53-39 X 3,098,916 7/1963 Souligney 5339 X 3,119,216 1/1964 Held 5339 3,299,604 1/ 1967 Kraut 20678 TRAVIS s. MCGEHEE, Primary Examiner E. F. DESMOND, Assistant Examiner 

